1. Field of the Invention
The present invention relates to a high frequency switch and a composite high frequency component including the same. Particularly, the present invention relates to a low-voltage control high-frequency switch that switches a transmission/reception signal with a low control voltage and a composite high frequency component.
2. Description of the Related Art
High frequency switches that transmit/receive transmission/reception signals of a plurality of communication systems having different frequency bands with an antenna and switches the transmission/reception signal into transmission signals and reception signals, and composite high frequency components having the same are known.
The high frequency switch includes a plurality of diodes that output transmission signals to an antenna and input reception signals from the antenna into a receiving unit (e.g., Japanese Unexamined Patent Application Publication No. 2000-165274).
Here, the structure of a composite high frequency component described in Japanese Unexamined Patent Application Publication No. 2000-165274 is described with reference to FIG. 1.
The composite high frequency component is applied to GSM1800 (DCS) of an 1800 MHz band, GSM1900 (PCS) of a 1900 MHz band, GSM850 of an 850 MHz band, and GSM900 (EGSM) of a 900 MHz band.
In FIG. 1, a diplexer (multiplexer/demultiplexer) 102 multiplexes and demultiplexes a transmission/reception signal of a GSM850/GSM900 system and a transmission/reception signal of a GSM1800/GSM1900 system. A transmission/reception selector switch 103 switches the transmission signal and the reception signal of the GSM850/GSM900 system. Similarly, a transmission/reception selector switch 104 switches the transmission signal and the reception signal of the GSM1800/GSM1900 system. A filter 105 allows the fundamental harmonic of the transmission signals of the GSM850/GSM900 system to pass therethrough to attenuate the harmonics. Similarly, a filter 106 allows the fundamental harmonic of the transmission signal of the GSM1800/GSM1900 system to pass therethrough to attenuate the harmonics thereof.
In the transmission/reception selector switch 103, a diode GD1 and an inductor GSL1 are disposed on a transmission line through which the transmission signal of GSM850/900 is transmitted and the diode GD1 is disposed in series on the transmission line of the transmission signal. On a transmission line through which the reception signal of GSM850/900 is transmitted, a strip line GSL2, a diode GD2, and a capacitor GC5 are disposed, and the diode GD2 is disposed in shunt to the transmission line of the reception signal. The two diodes GD1 and GD2 are connected in series so that a direct current flows into the two diodes GD1 and GD2 when a positive voltage is applied from a terminal VcG for a transmission/receiving selection control signal.
Similarly, in a transmission/reception selector switch 104, a diode DD1 and an inductor DPSL1 are disposed on a transmission line through which the transmission signal of GSM1800/1900 is transmitted and the diode DD1 is disposed in series to the transmission line of the transmission signal. On a transmission line through which the reception signal of GSM1800/1900 is transmitted, a strip line DSL2, a diode DD2, and a capacitor DC5 are disposed and the diode DD2 is disposed in shunt to the transmission line of the reception signal. The two diodes GD1 and GD2 are connected in series so that a direct current flows into the two diodes DD1 and DD2 when a positive voltage is applied from a terminal VcD for a transmission/receiving selection control signal.
The composite high frequency component is used for a communication device in a mobile communication system, such as a cellular phone terminal. With a recent demand for reduction in power consumption, a driving voltage is also increasingly reduced. However, when the voltage of a control signal of a transmission/reception selector switch (high frequency switch) as illustrated in FIG. 1 is reduced, a voltage applied between an anode and a cathode of the two diodes (e.g., diodes GD1 and GD2 in the transmission/reception selector switch 103 for GSM850/900 illustrated in FIG. 1) is close to a PN junction potential of the diodes. Under such conditions, the diodes are not in a perfect-conducting state, and a phenomenon such that the ON-resistance increases or a voltage across the diode fluctuates depending on a voltage of a transmission signal to be transmitted/blocked arises. Therefore, problems arise with circuit characteristics such that insertion loss (IL) deteriorates and harmonic distortion increases. Therefore, there is a limitation on the amount that a control voltage can be reduced.
The above-described problems similarly arise in, for example, a reception signal selector switch that switches reception signals of two communication systems having mutually different frequency bands, and not only in the transmission/reception selector switch.